PHP 5.2.1, IIS 6, Win2K3 Server, and COM...?

I have some PHP code that I wrote to manipulate Excel workbooks. It works fine on my old server which was running Apache 1.x and Win2K. I can also get the code to execute using PHP on the command line. For some reason, it will not work through a web browser, only the command line on the new server. I think I might have something misconfigured on IIS. Any ideas on what could be wrong?